What horror movies really do to your body.. MORE: In the study, published in British journal The BMJ, researchers recruited 24 healthy volunteers aged 30 or younger. Fourteen of the volunteers watched a scary movie (Insidious), and then a week later a light, educational movie (A Year in Champagne). The remaining volunteers did the reverse, watching the tame movie first, and then the suspenseful one.
Researchers found that while watching Insidious, the volunteers’ levels of factor VIII—a protein that plays a role in blood clotting—jumped by enough to raise their risk of blood clots; 57 percent of the volunteers experienced the jump, while just 14 percent experienced an increase during the educational movie. (If you’re not a fan of scary movies, there’s an explanation why.)..